This invention pertains generally to telephony, and more particularly to telephony over digital data networks.
Plain-old telephone service (POTS) has existed now for well over 100 years. During that time, people have grown used to the limited sound quality of POTS. At the outset of the telephone era, these limits on sound quality were due largely to the telephone""s simple transducers and the transmission effects of long analog lines. As better transducers and compensation (gain and filtering) for transmission line effects became available, multiplexing transmission techniques also were introduced. These transmission techniques relied on the traditional limited audio bandwidth for voice communication, and thus the traditional limits on telephone sound quality remained.
As the public-switched telephone network (PSTN) evolved into a largely digitally-switched system between the 1960s and today, limited audio capabilities were maintained. The T1 digital carrier format, which is virtually ubiquitous within the PSTN today, relies on the appearance, at a PSTN analog-to-digital converter, of an analog telephone audio signal with a highest frequency of less than about 3500 Hz (sampled at 8 kHz and brick-wall filtered below 3500 Hz). Standard telephone handsets also cut off low-frequency transmissions to reduce 60 Hz power-line hum and other interference. These constraints limit the actual audio frequency range for a typical POTS phone conversation to 300-3400 Hz.
Packet-switched data networks now offer an alternative to PSTN telephony. Two computer users connected to a packet-switched data network can communicate data in any format that both understand. This includes packetized, digitized telephony in a variety of formats, including some offering stereo sound with a frequency range much larger than that offered by the PSTN and the standard POTS telephone. Due to cost and availability, current IP telephony equipment also uses traditional narrowband handsets.
Integrated telephony/high speed data access technology is now entering the marketplace. With this technology, a single wide-area-network (WAN) connection allows simultaneous packet data and packetized POTS telephone transmissions.
A packetized POTS transmission from a first integrated phone/data transceiver terminates either at a PSTN gateway (either digital or analog), or at a second integrated phone/data transceiver. The present invention recognizes that a packetized POTS transmission may be processed differently depending on how it terminates. For instance, if it terminates at a PSTN gateway, sound quality commensurate with the PSTN is all that makes sense. But if it terminates at a packetized POTS receiver, a much richer sound quality may be possible.
The present invention describes a telephone to digital data network interface. The interface comprises a telephone connection point (such as an RJ11 jack, electrical terminal pair, or a wire with an RJ11 plug) connected to a first selectable interface audio processing path for telephone-grade audio communication. The interface also comprises a second selectable interface audio processing path for wideband audio communication. An audio quality selector monitors the first processing path for the presence of switchover commands, and selects a desired audio processing path based on such a command when it is received from a telephone connected to the telephone connection point. Thus both standard telephone-grade and wideband telephony are available to the user and selectable from an attached telephone.
The telephone connection point preferably comprises an analog telephone line interface accepting a POTS phone. Preferably, the two audio processing paths use different digital audio decodersxe2x80x94one for wideband and one for telephone-grade audio. The second audio processing path preferably bypasses the telephone connection point, and, e.g., provides a connection for a headset, a stereo or television audio input, or a computer.
In another aspect, the invention provides a method of operating an analog telephone/digital data network interface. The method comprises the step of presenting a standard analog telephone line interface to an attached telephone set. But the interface detects a signal produced at the standard analog telephone line interface by the attached telephone set, and responds to the signal by reconfiguring audio processing between a telephone-grade processing path and a wideband processing path within the telephone/data network interface. Preferably the signaling is performed with DTMF codes, hookswitch flashes, voice prompts and commands, or a combination of these signaling techniques.
In yet another aspect, a cable modem transceiver is disclosed. This transceiver has connection points for remote data, local data, a telephone, and wideband audio. The transceiver further comprises a telephone to digital data network interface that has multiple switchable audio outputs, one of the switchable audio outputs connected to the telephone connection point and another of the switchable audio outputs connected to the wideband audio output connection point. The transceiver also comprises a bridge that routes data between the remote data connection point, the local data connection point, and the telephone to data network interface.